Draft regulations for mandatory diesel particulate control measures on heavy vehicles operated by the state are in the process of being finalised by the California Air Resources Board (CARB).

The regulations, which represent the third set of fleet rules considered by CARB as part of their reduction programme, date back to initial recommendations made in October 2002 for urban transit buses and refuse truck fleets.

The proposal on control measures for publicly owned and operated fleets covers all 1960 to 2006 model year heavy-duty diesel engines owned, operated, or contracted for operation by municipalities in vehicles over 14,000 lb gross vehicle weight rating.

Pioneering restrictions on school buses have already made headlines in the US, with the American diesel retrofit emission-reduction market expanding rapidly.